But didn't a train derailment happen that may have been caused by this?
Depending on what you mean by "this" - not that I am aware of. There was an derailment off the new Wodonga bypass in 2010, but that was caused by a rolling stock issue. There have been train partings where track condition may have contributed to the parting, but for some of those partings at least there were more significant contributing factors.
If you go back in time you will find derailments caused, in part, by poor sleeper condition. Installing concrete sleepers addresses that.
If for example , ARTC was in someway negligent or used innapropriate measures in relation to the track upgrading, who would determine this?
If there may have been a breach of regulations or laws, the relevant regulator (which one depends on specifics) would take the company and/or its directors and/or executives to court.
If it is just a commercial issue between ARTC and an operator, then the access agreement between ARTC and the operator sets out limits and an approach towards determining liabilities and a dispute resolution process.
Yep ATSB does the investigation. You would be aware that with aviation were ATSB conducts most of it's investigations and recommendations may be made to CASA.
They may make recommendations to whoever they choose, not just the regulators. There's no legal requirement for the recipient of the recommendation to actually follow the recommendation, but the response of the recipient to the recommendation is made public.
It goes back to how ARTC was set up to start with. Expected to be a commercial enterprise (not a Not for Profit like state authorities).
I don't see how that is relevant at all to either a) the pre-existing condition of the track, or b) the funds made available through grants for upgrades and repairs. ARTC is clearly not a short or medium term commercial proposition. The set-up as a federal-owned corporation is for transparency (it is easier to understand how much money is being collected and spent across the network) and to give the rail industry as a whole more control over the network.
Some of the comments in this thread indicate a lack of understanding about the financial and operational constraints associated with the interstate rail network. There isn't a magical money tree; and nor should there be.